In a motor-vehicle engine system, fuel from a fuel tank is intended to flow to the combustion chambers of the engine with unit efficiency, such that no fuel is released into the atmosphere. In practice, various measures are taken to recapture fuel that has escaped its intended flow path and might otherwise be released into the atmosphere as vapor. Such fuel is typically redirected to the intake manifold of the engine.
For instance, a positive crankcase ventilation (PCV) system may be used to recapture and combust fuel vapor that has entered the crankcase. In addition, fuel vapor vented from the fuel tank (whether the motor vehicle is operating, resting, or being refueled) may be temporarily trapped in an adsorbent canister and delivered to the intake manifold during a subsequent purge of the adsorbent canister. In motor-vehicle engine systems used today, the crankcase and adsorbent canister, maintained near atmospheric pressure by coupling to an air cleaner, may each communicate with the intake manifold via a control valve. The vacuum that may be present at the intake manifold provides a motive force to draw fuel vapor from the crankcase and/or adsorbent canister and into the engine, where it is combusted.
Crankcase ventilation and fuel-vapor purging as described above may be effective and reliable so long as sufficient vacuum is available at the intake manifold. In boosted engine systems, however, sufficient vacuum may be unavailable during some operating conditions, such as during medium- or high-level boost. One solution to this problem is to provide a supplementary source of vacuum such as an electrically driven vacuum pump to purge fuel vapor from the crankcase and/or adsorbent canister when intake manifold vacuum is not available. However, this approach increases engine-system cost and complexity.
Alternative approaches independently provide crankcase ventilation or adsorbent-canister purging driven by positive pressure instead of manifold vacuum (e.g., U.S. Patent Application Publication Number 2008/0083399, and U.S. Pat. No. 7,284,541, respectively). However, the inventors herein have recognized that it can be advantageous to coordinate positive pressure crankcase ventilation and positive pressure adsorbent canister purging. Therefore, one embodiment provides a method for combusting a vapor of a fuel accumulated in a crankcase of an engine, the engine disposed in a vehicle having a fuel tank and an adsorbent canister coupled to the fuel tank. The method comprises flowing compressed air from a first air source through the crankcase to yield a crankcase effluent enriched in gasses leaked from the combustion chamber, which include the fuel vapor. The method further comprises combining the crankcase effluent with an effluent from the adsorbent canister, also enriched in the vapor, and, flowing the combined crankcase and adsorbent-canister effluent to an intake of the engine via a conduit. This method address the disadvantages noted above, and further provides that engine surfaces subject to accumulation of engine lubricant from the crankcase effluent (compressor blades, EGR coolers, etc.) are protectively scrubbed by the adsorbent-canister effluent, thereby reducing the tendency of the engine lubricant to foul these surfaces.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.